Process of production of dehydrolinalyl acetate (I)

ABSTRACT

The present invention is related to a novel and improved process for the production of dehydrolinalyl acetate (DLA), which IUPAC name is acetic acid 1-ethynyl-1,5-dimethyl-hex-4-enyl ester, starting from dehydrolinalool (DLL), which IUPAC name is 3,7-dimethyloct-6-en-1-yn-3-ol, by catalytic acetylation.

This application is the U.S. national phase of International ApplicationNo. PCT/EP2014/059363 filed 7 May 2014 which designated the U.S. andclaims priority to EP Patent Application No. 13166960.8 filed 8 May2013, the entire contents of each of which are hereby incorporated byreference.

The present invention is related to a novel and improved process for theproduction of dehydrolinalyl acetate (DLA), which IUPAC name is aceticacid 1-ethynyl-1,5-dimethyl-hex-4-enyl ester, starting fromdehydrolinalool (DLL), which IUPAC name is3,7-dimethyloct-6-en-1-yn-3-ol, by catalytic acetylation.

Dehydrolinalyl acetate (compound of formula (I))

is an important and valuable compound for the use in the field offlavour and fragrance applications.

DLA can also be used in the production of linalylacetate (compound offormula (IV))

which is also an important and valuable compound for the use in thefield of flavour and fragrance applications.

Nowadays, DLA is usually produced by an acetylation of DLL by usingp-toluene sulfonic acid as an “organic-soluble” acid catalyst.

In course of this reaction significant amounts of side products, such asD,L-iso-3,7-dimethyl-7-octen-1-in-3-yl acetate (iso-DLA; compound offormula (V)),

2,2,6-trimethyl-6-ethynyltetrahydropyrane (ETTP; compound of formula(VI))

and 3-isopropenyl-1-methyl-2-methylene-cyclopentylacetate (compound offormula (VI))

are formed.

The goal of the present invention was to find an improved process forthe production of DLA, without the above mentioned disadvantages of theprocess of the prior art (especially reducing the amount of the sideproducts).

Surprisingly it was found that when a very specific type of catalyst isused, DLA is obtained by the acetylation of DLL with a significantlylower amount of undesired side products and with excellent selectivityand yield.

Therefore the present invention is related to the process of productionof DLA, which is the compound of formula (I)

by reacting DLL, which is the compound of formula (II)

with acetic anhydride, which is the compound of formula (III)

characterized in that the process is carried in the presence of at leastone catalyst of formula (VIII)wherein

M signifies a 3d element or a 4f element from the periodic table and xis 2, 3 or 4.

3d elements comprise 10 chemical elements with atomic numbers 21 through30 (from scandium through zinc).

4f elements are lanthanoide elements and comprise fifteen metallicchemical elements with atomic numbers 57 through 71 (from lanthanumthrough lutetium).

Preferred are catalysts of formula (VIII), wherein M is Sc, wherein x is3 or Zn wherein x is 2.

In the process according to the present invention the catalyst (or themixture of catalyst) is usually used in very low amount. Usually it isused in a ratio of 1000:1 up to 100,000:1 (compound of formula (II):catalyst). Preferably the ratio of compound (II) to catalyst is 10,000:1up to 50,000:1.

The process according to the present invention is usually carried out atelevated temperatures.

Preferably the process according to the present invention is carried outat a temperature of 30-70° C., more preferably 30-60° C.

The process according to the present invention is usually carried out atnormal pressure.

DLL and acetic anhydride (Ac₂O) can be added to the reaction mixture inequimolar amounts. It is also possible to use slight excess of eitherone of the compounds. Usually the acetic anhydride is used in a slightexcess in regard to DLL. Preferably acetic anhydride (compound offormula (III)) is added in a ratio of 1:1 up to 3:1 (in regard tocompound of formula (II)). More preferably acetic anhydride (compound offormula (III)) is added in a ratio of 1.1:1 up to 2:1 (in regard tocompound of formula (II)).

The process according to the present invention is usually carried outwithout any solvent(s). But it would also be possible to use an inertsolvent (or mixture of inert solvents).

Preferably the process according to the present invention is carried outwithout any solvents.

The starting material (compound of formula (II) and compound of formula(III)) can be mixed together before the process is started or one of thestarting material can be added to the other while the process is goingon.

Usually the compound of formula (II) and the catalyst are mixed and thenthe compound of formula (III) is added to the reaction mixture during aperiod of time.

After the addition and mixture of all the starting material the reactionmixture is let reacted for some time.

Usually the reaction time for the process according to the presentinvention is between 2 to 10 hours.

At the end of the reaction, the reaction mixture is usually neutralizedand the remaining acetate anhydride and the acetic acid (product of theprocess) are removed from the reaction solution. This is usually done bydistillation (normal pressure or at a reduced pressure).

The DLA which is obtained by the process according to the presentinvention can be used as such (flavour and fragrance applications) or itcan be used in the production of other useful compounds, especiallylinanylacetate (obtained by hydrogenation of DLA).

The following examples serve to illustrate the invention. If nototherwise stated all parts are given are related to the weight and thetemperature is given in ° C.

EXAMPLES Example 1 Zn Triflate as Catalyst

Into a 350 ml four necked round bottomed flask fitted with a thermometerand a reflux condenser 162.2 g DLL (1.06 mol) and 15.3 mg of Zinctrifluoromethane sulfonate (0.042 mmol) were placed. Within 1 h, 120 ml(1.27 mol) Ac₂O were added under stirring.

The yellowish reaction solution was heated to 45° C. (oil temperature),the reaction temperature increased until 50° C., after 8 h the reactionmixture was neutralized with 0.5 g sodium carbonate, cooling to roomtemperature. The Ac₂O and AcOH-mixture was distilled at 150 mbar at 75°C.

211.3 g a yellowish liquid was obtained and contained 1.6 w % DLL, 0.3 w% iso-DLA, 92.6 w % DLA, 0.2 a % AcOH and 0.7 a % Ac₂O.

Total conversion: 97.9% and total yield: 95.6%.

Example 2 Sc Triflate as Catalyst

The same reaction conditions were used. But instead of Zinctrifluoromethane sulfonate Sc trifluoromethane sulfonate was used.

Total conversion: 91.6% and total yield: 87.9%. (only 0.1 wt-% ofiso-DLA was obtained).

Other catalysts were tested

Pyridine, H₃PO₄, H₂SO₄, CH₃SO₃H, (CF₃SO₃)₂O, CF₃SO₃H, (CF₃SO₃)₂Mg,CF₃SO₃Ag and (CF₃SO₃)₂Ca.

None of these catalysts have shown the same properties in the reactionas the catalyst according to the present invention.

The invention claimed is:
 1. A process for the production ofdehydrolinalyl acetate (DLA) which is a compound of formula (I):

 wherein the process comprises reacting dehydrolinalool (DLL) which is acompound of formula (II):

with acetic anhydride which is a compound of formula (III):

in the presence of at least one catalyst of formula (VIII):

 wherein M is Zn and x is 2 or M is Sc and x is
 3. 2. The processaccording to claim 1, wherein the DLA and the catalyst are present in aratio of DLA to catalyst of 1000: 1 up to 100,000:1.
 3. The processaccording to claim 1, wherein the process is carried out at atemperature of 30-70° C.
 4. The process according to claim 1, whereinthe process is carried out at normal pressure.
 5. The process accordingto claim 1, wherein the DLL and the acetic anhydride are present in aratio of the acetic anhydride to DLL of 1:1 up to 3:1.
 6. The processaccording to claim 1, wherein the process according is carried out inthe absence of solvents.
 7. The process according to claim 1, whichfurther comprises neutralizing a reaction mixture containing the DLA andremoving any remaining acetate anhydride and the acetic acid from thereaction mixture.
 8. The process according to claim 2 wherein the ratioof DLA to catalyst is 10,000:1 up to 50,000:1.
 9. The process accordingto claim 3, wherein the process is carried out at a temperature of30-60° C.
 10. The process according to claim 5, wherein the ratio ofacetic anhydride to DLL is 1.1:1 up to 2:1.